The objective of this study is to provide some fundamental data regarding degenerative and possible regenerative changes in the mammalian central nervous system. The first part of the study will be concerned with the rates of Wallerian degeneration in the spinocervical, dorsal spinocerebellar, and ascending proprio-spinal tracts after lesions of the lumbar spinal cord. The fiber analysis will be done on material processes for electron microscopy and stained with Azur II- methylene blue. The second part of the studywill be concerned with a quantitative study of the retrograde neuronal changes in Clarke's column and will relate to the degree of neuronal death and chromatolysis to the age of the animal, the post-operative survival period, and the amount of axoplasm destroyed. Data will be obtained from neuron counts of material stained by the Nissl method. The third part involves a study of axonal sprouting of dorsal roots in the spinal cord after chronic partial deafferentation of several systems and utilizes the Nauta-Gygax and Fink-Heimer silver methods in conjunction with the autoradiographic methods for tracing neuroanatomical connections. This part of the investigation is being undertaken because of controversy regarding the contradictory evidence for sprouting as seen in light microscopic studies in the adult animals and to try to determine whether a significantly greater degree of plasticity of the CNS is present at earlier stages, a hypothesis that would appear to have probability.